1. Field of the Invention
This invention relates to extrusion dies for extruding material through a plurality of die orifices. It especially relates to extrusion dies for extruding catalytic mix materials into catalyst particles of uniform size and shape.
2. Prior Related Art
In many commercial applications, catalysts are relied upon to aid in accelerating or inhibiting chemical reactions. Oftentimes, the catalysts are produced by passing a suitable catalytic mix material through an extrusion machine incorporating an extrusion die having a plurality of die orifices therein of equivalent cross-sectional area and of the same cross-sectional shape. The catalytic material extruded through such a die is forced out of the orifices in streams of extrudate. These streams are subsequently cut at uniform time intervals to produce catalyst particles, which are herein termed catalyst extrudates.
In most commercial applications, catalyst extrudates are used in the form of packed beds. However, it has been found that the pressure drop through a bed of catalyst extrudates can be reduced by making the extrudates of uniform size and shape. But as presently produced on a commercial scale, catalyst extrudates are of varying sizes, primarily because the catalytic mix material processed through commercial extrusion machines does not pass through all of the die orifices at the same rate. The linear velocity of material extruded through the orifices in the central portion of an extrusion die is greater than that of the material extruded through the orifices near the periphery thereof. This result is largely due to the laminar flow characteristics of the catalytic mix material just prior to extrusion through the die. Because of this difference in linear velocities, when all the extruded material is cut at a specified distance from the external die face at uniform time intervals, the catalyst extrudates produced from material that originally passed through orifices in the central portion of the die will necessarily be longer than those produced from material that originally passed through the orifices near the periphery.
Accordingly, it is a specific object of this invention to provide a die having orifices arranged therein such that the extrusion material will pass through all the orifices at an essentially uniform linear velocity.